Automatic telephone system



W. T. POWELL AUTOMATIC TELEPHONE SYSTEM Dec. 13, 1927.

2 Shee To NEAT F'HDER INVENTOR s9 \N\NFRED T POWELL TEE: REVERTIVE CALLFWDER BY A.

XZDWF 9506.50

Filed March l4. 1921 a". ZR EQUEHCY SELECTOR.

ATTORNEY Dec. 13, 1927. PoyvE L' AUTOMATIC TELEPHONE SYSTEM Fired MarchM. 1921 FIGE 52 m jl sL z h n 2 I MU I CONTr\CT RELAYS.

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I IIII FINDER BRIDG FINDER ALLOTTER" TEHE REGISTER DATTT} MAIN EXCHANGEI I I l I I I INVENTOR 1 I WINFRED T OW I BY -W ATTORNEY FIGS AT TENDAHTS STAT \OH.

Patented Dec. 13, 1927,

UNITED STATES PATENT OFFICE.

WINFRED T. POWELL, OF ROCHESTER, NEW YORK, ASSIGNOR TO THE STROMBERG-CARLSON TELEPHONE MANUFACTURING COMPANY, OF ROCHESTER, NEW YORK, A

CORPORATION OF NEXV YORK.

AUTOMATIC TELEPHONE SYSTEM.

Application filed March 14, 1921.

This invention relates to telephone sys tems and more particularly totelephone systems employing automatic switches in com-.

pleting some part of a telephone connection. The main feature ofthepresent invention is an improved method of interconnecting telephonelines through the use of non-numerical switches only.

An additional feature of this invention is it the provision of means forsignalling party lines in such a telephone system.

A further feature of the invention relates to novel means for completingrevertive calls, that is, calls between stations on the same 1 telephoneline.

the dotted lines extending across this figure,

represents a very abbreviated disclosure of a second telephone line andthe non-numerical switch individual to said line, but in this instancethe four substations of the line are M only indicated. The portion ofthe drawing below this last mentioned telephone line represents anon-numerical finder switch, a numerical frequency selector and Variouscircuits associated therewith which are emit? ployed in the case of ar-evertive call to intermittently and alternately signal the calling andcalled stations. At the upper lefthand corner of Figure 2. there isrepresented a talking bridge or link of which there are suflicient tocare for the maximum number of simultaneous conversations. At thelefthand side of Figure 2 and set off by dotted lines there isrepresented a bridge or link allotter switch which, as the namesignifies,

4 operates to assign an idle bridge or link circuit for use. Near thecenter of Figure 2 and set oil by dotted lines there appears a finderswitch, of which there are sufficient to care for the maximum number ofcalls that are in so the process of being completed. There is associa'ted with each one of these finders. a sender which includes a tensregister and a units register which appear at the lower right-handcorner of Figure 2. At the up- Serial No. 451,961.

per right-hand corner of Figure 2 there are represented threemulti-contact test relays, but it will be understood that ten suchrelays are provided in a system of 100 lines and that each of theserelays is provided'with ten distinct sets of contacts. At the lowerleft-hand corner of'this figure there appears a finder allotter whichfunctions to assign an idle finder as well as its associated registersender for use.

Figure 3 represents an attendant opera tors station andshows a portionof an individual line switch assigned to that station. A portion only ofthe incoming'trunk and of the operators equipment are indicated, but itwill be understood that the portions which have been omitted may bearranged after the manner of that now in use.

The switches which are employed in this system may be of substantiallythe same structure as that disclosed in the patent to Clement. 1,107,153patented August 11. 1914.

It is believed that the invention will best be understod by describingthe operation of establishing a telephone connection from substationsuch as that indicated at A to a called line such as that indicated atB, which it is assumed is designated #88.

When the subscriber at A removes his receiver from its switch-hook. acircuit is closed from grounded battery through the left-hand Winding ofline relay 1, inner back contact and armature of the cut-off relay 2over the lower side of the calling line and through the callingsubstation circuits, over the upper side of this line and through theuppermost armature and back contact of the cut-off relay 2 to ground.The line relay is energized in this circuit and closes an operatingcircuit for the motor magnet 3 extending from ground, winding of thismagnet through the ofi'normal contacts 4, armature, front contact andright-hand winding of the line relay, armature and back contact of themotor magnet, resistance to grounded battery. Under the control of thiscircuit the motor magnet advances the brushes of the line switch onestep thereby opening the off-normal contacts 4 and closing theoff-normal contacts 5. This completes a circuit for the motor magnet nowtraceable from ground, winding of this magnet. off-normal contacts 5.lowermost armature and back contact of the cut-off relay 2, armature andback contact of the motor magnet, through the resistance to groundedbattery; Under the control of this last-described circuit, the motormagnet advances the brushes of the line switch until an allotted link orbridge circuit is reached, at which time the motor magnet isshort-circuited by a circuit completed from grounded battery, resistanceback contact and armature of the motor magnet, right-hand winding of thelinerelay l, left-hand front contact and armature of this relay, upperlow resistance winding.

of the cut-off relay 2, armature and back contact of the relay 6, testbrush 7, test conductor 8, lower back contact and armature of the slowreleasing relay 9, brush 10 of the bridge allotter, inner armature andback contact of relay 11, upper back contact and armature of relay 12 toground.

This last described circuit is also effective to energize the cut-01frelay 2 which disconnects the line relay 1 from the calling lineand-alsoopens the operating circuit of the motor magnet 3 at thelowermost armature andback contact of this relay. When the cut-01f relayoperates to extend the calling line through brushes Band 1% of the lineswitch to'conductors and 16 thereby completing the impulse circuit,conductor 15 extends the impulse circuit through the up permostarmatureand back contact of relay 17 lower winding of relay 18 togrounded battery, while conductor 16 includes the other side of impulsecircuit which extends through the lower back contact and armature ofrelay 17 and through the upper winding of relay 18 to ground. As aresult of the closing of this circuit, relay 18 attracts'jits armaturesand thereby closes a circuit for energizing the slow re'leasing relay 9'from grounded battery, winding of this relay, up

per front contact and armature of relay 18; conductor 19, lowresistance'winding of relay 11 to ground. Relay 11, however, isshortcircuited by ground at the inner armature and back contact of arelay 9 of an idle' bridge. Relay 9 thereby closes aholding circuit forthe'line switch extending from ground, its inner upper armature andfront contact upper armature and back contact of the holding relay 20,outer backcontact and armature of relay 87, conductor 21, holding brush22 of the line switch, inner lower armature, front contact and the highresistance winding of the cut-off relay 2 to grounded battery. Relay 6is alsoenergized in a circuit in multiple of that justdescribed whichextends to grounded battery through the lower winding of this relay. Assoon as relay 9 is actuated, it closes at its uppermost armature acircuit for energizing the relay 78. It shouldbe noted at this pointthat contacts designated X on relay 9 are closed before contacts Y areopened.

In the usual operation of the system such a bridge circuit as thatdescribed is' in readiness to receive a call. This is due to the factthat as soon as the holding relay of any bridge circuit is energizedupon the location of this bridge by an allotted Te finder, a circuit isclosed from ground, lower armature and front contact of the operatedholding-relay, conductor 23, brush 24 of the bridge allotter, backcontact and armature of the motor magnet 25 of this allotter,

outer armature and back contact of relay 11, Winding of magnet 25 togrounded battery. The motor magnet 25 will thus advancethe brushesof-the bridge allotter as long as the brush 24 engages the terminalhaving a ground potential thereon due to the energizetion of a holdingrelay 20 of engaged bridge circuits. lVhenever an idle bridge isreached,the motor magnet 25 will remain inert until the allotted bridge isseized by some succeeding calling line. Also when the line'relay 1 isenergized on the initiation of a call it closes a circuit for relay 26includingthe conductor 121. With the relay 26' energized a circuit iscompleted from ground through its left-hand armature and front contact,brush 27 of the finder allotter, back contact, armature and winding ofthe motor magnet 28 of the allotted finder switch through resistance 29,back contact and armature of re--- I lay 30 to grounded battery. Underthecontrol of this circuit the finder will advance its brushes 31, 32,33 and 34 until its brush 31 encounters a terminal individual to theallotted bridge circuit, at which time the relay contact of a relaysimilar to 30 of an idle finder switch, over conductor 37, winding ofrelay 30,'righthand winding of relay 35, inner armature and frontcontact of this relay, conductor 38, finder brush 32, outer back contactand armature of the ringing relay 39, outer back'contact and armature ofrelay 40, lower winding of relay 20, inner front contact and armature ofrelay 9 to ground. Relays 30 and 20 are energized and relay 35 heldenergized in this circuit. The high resistance rlght-hand-winding ofrelay 35 serves to hold it operated aslong'as'its finder switch is inuse even after the bridge allotter has advanced to some other position.The release relay is energized in a lit) circuitin multiple of that lastdisclosed, and at its left-hand armature and front contact closes alocking circuit for itself independent of the control of the relay 35.With relay 60 operated an energizing circuit is closed for relay 59 fromgrounded battery, its Winding, outer back contact and armature of relay54, conductor 61, outer front contact and armature of relay 60 toground. WVhen relay attracts its armature it closes a circuit fromgrounded battery, brush 41 of the finder allotter, winding of relay 42to ground. This energizes relay 42 and closes a circuit for the motormagnet 143 of the finder allotter, from grounded battery, inner armatureand front contact of relay 42, winding back contact and armature ofthis. magnet, lower armature and back contact of relay 12, back contactand armature of relay 26 to ground. Under the control of this circuitthe motor magnet 143 advan the brushes of the finder allotter until itsbrush 41 encounters the terminal individual to a finder switch that isidle, at which time relay 42 deenergizes and opens the operating circuitof the motor magnet 143.

The operations just described have been effective to connect the callingline to an idle bridge circuit and to connect an idle register sender tothis link circuit through the brushes of its associated finder switch.The remaining operations have allotted another bridge circuit for thenext call that it originated, and have advanced the finder allotier toassign an idle finder and its associated register sender for use in thenext succeed: ing call.

The apparatus is now in condition to receive the impulses correspondingto the designation of the wanted line. The first series of impulsestransmitted is effective to select the proper frequency for ringing thebell at the wanted station on the called line, and consists of either 2,3, 4 or 5 impulses, depending upon whether 16, 33, 50 or 66 cycleringing current is selected. Let it be assumed that the bell at thewanted station responds to 16 cycle ringing frequency, wherefore inorder to select this fre quency, the calling party operates his dialsender to transmit two impulses of current. In response to theseimpulses the impulse relay l8 retracts its armature twice and on eachretrcdio'n closes a circuit from ground, lower arrltllltf and frontcontact of relay 20, lower back contact and armature of relay l8,conductor 43, brush 44 of the frequency selector in its normal position,winding of slow releasing relay 45, winding of the motor magnet 46 togrounded battery. The slow releasing relay is energized in this circuitand is maintained energized dur ing this firs series of impulses, butthe motor magnet is operated in response to each of these impulses andadvances the brushes her corresponds to the tens digit of the vwantednumber, and in response to each of these impulses the impulse relay l8vibrates armatures and now closes a circuit from ground, lower armatureand front contact of relay 20, lower back contact and armature of relay18, conductor 43, brush 44 of the frequency selector switch armature andback contact of relay 45, conductor 4?, brush 34,

of the finder switch, continuity spring and back contact of change-overrelay 48, outer armature and front contact of relay 35, winding ofchange-over relay 48, conductor 49, winding of the motor magnet togrounded baits U The change-over relay 48 is operated in this circuitand the impulse circuit is thereby extended through the continuityspring and armature of relay 48 which renders the circuit independent ofthe control relay 35. In response to each impulse of the tens series themotor magnet 50 advances the brushes of the tens register one step, butat the close of the tens series of impulses the change-over relay 48 ofthe tens. register deenergizes and the senderis in condition. to receivethe units series of impulses. As soon as the brush 122 of the tensregister is moved from its normal position, the right-hand winding ofrelay 35 is short circuited, and since the bridge allotter has beenmoved to a bridge other than that under consideration, the circuitincluding the left-hand winding of relay 35 is opened and itdeenergizes.

The units impulses, which are eight in number, are repeated to the unitsregister over a circuit closed from ground, armature and front contactof relay 20, back contact and armature of relay 18, conductor 43, brush44, armature and back contact of relay 45, conductor 47, finder brush34, continuity spring and back contact of relay 48, outer armature andback contact of relay 35, continuity spring and back contact of unitschange-over relay 51, the units register brush 52 in its first position,winding ofthe change-over relay 5i, winding of the motor magnet togrounded battery. The changeover relay 51 is energized in this circuitand extends the impulse circuit through its continuity spring andarmature which renders this circuit independent of the register brush Inresponse to each of the im pulses repeated over this circuit, the motora la register one step until the close of this series of impulses whenthe relay 51 retracts its armatures, and if no other sender is testingany of the lines of the system, the sender under consideration tests thewanted line to determine whether it is busy or idle.

Let it be assumed that no other sender is testing any of the lines,under which assumption the relay 54 of the sender under consideration aswell as the relays 54 and 54 will be inactive. Relay 54 is now operatedin circuit completed from ground, continuity spring and back-contact ofrelay 54 through the continuity springs and back contacts of othersimilar relays at the other register senders, back contact and left-handcontinuity spring and winding of relay 54, conductor 55, back contactand armature of relay51, units register brush 56 which we will assumehasbeen advanced to its eighth position, multi-contact relay 58 of thegroup of lines in which the called line is located. The relay 54 opensthe ei'iergizing circuit of relay 59 but before this relay retracts itsarmature, a test circuit is closed from ground at the outer armature andfront contact of release relay 60, conductor 61, outer armature andfront contact of relay 54, continuity spring and armature of relay 59,upper winding of relay 62, tens register brush 3 in its eighth position,conductor 64, innermost armature and front contact of relay to the testwire 65 of line #88, upper winding of relay 66, upper back contact andarmature of cut-off relay 67, left-hand winding of line relay 68 togrounded battery. The relay '66 attracts its armature and renders thetest brush 72 ineffective totest the outgoing terminals of bridgecircuits, but when this'brush reaches the group of incomin terminals ofthe brid e circuits a contact 71 will be closed to render the test brush72 effective. l/Vith line relay 68 energized the motor magnet 69 of thecalled line switch is operated to seize the bridge circuit to which thecalling line is connected.

When the terminating line switch reaches the bridge circuit to which thecalling line has been connected, a circuit isclosed from groundedbattery, resistance, contact and armature of motor magnet 69, right-handwindingof line relay 68, its front contact and armature, upper windingof cut-off re- 67, lower ari'nature and front contact of relay 66,contact 71, test brush 72. test terminal 73, conductor 74, finder brush33, upper front contact and armature of relay 62, left hand winding ofrelease relay to ground. The cut-off relay 67 is energized in thiscircuit and closes a locking circuit for itself through its lower frontcontact andarmature, holding brush 75, test terminal 76, test conductor77, lowermost annature and front contact of relay 78, winding of ringingrelay 39 to ground. Relay 60 is differentially woundand releases becauseof the previouslydescribed circuit closed through its left-hand winding,and mentioned test circuit of the called line switch. lVith relay 6Odeenergized the motor magnet 50 of the tens register and the motormagnet of the units register are operated to restore these registers tonormal.

The ringing relay 89 is thus energized'andcloses a ringingcircuit fromthe source of 16 cycle ringing current, frequency selector brush 80,right-hand winding of the trlp relay -79, inner right-hand front contactand armature of relay 39 conductor 81 ring termina-l82 of the bridgecircuit, line switch brush 83 through the bell of the wanted station(not shown) over the upper side of the called line, tip brush 84, tipterminal 85, conductor 86, through the resistance, lefthand frontcontact and armature'of relay 39,- inner front contact andarmature ofrelay 78 to ground.

armature, and at its outer left-hand arma ture and front contact itshort-circuits the ringing relay 39 which deenergizes, whereupon alocking circuit is closed for the trip relay from grounded battery, itsleft-hand winding front contact and armature, lefthand back contact andarmature of relay 39, inner front contact and armature of relay T8 toground as soon as this last named relay is operated.

gaged when the test is made of this line after the settingofthe'register sender, the test circuit such as 'is open at the backcontact and inner upper armature of the cut-off relay 67 so that thecalled line switch'cannot be started to hunt for the bridged circuit towhich the calling line is connected. Also there will be no circuitcompleted for energizing the relay 62 of the finder (Fig. 2). The relay62 is inertand when relay 59 deenergizes after the test, a circuit isclosed for the relay 40. This circuit is traceablefrom grounded battery,winding of relay 40, its continuity spring and contact, lower frontcontact and armature of relay 18, conductor 43, brush 44, armature andback contact of relay 45, conductor 47,1[inder brush 34, lower backcontact and armature of relay 62, back contact and continuity spring ofrelay 59, leftkhand front contact and armature of relay 54, conductor61, outer Also when the calledp'artyresponds, the trip relay 7 9attracts its I Also when the called party responds, the relay 87 isenergized front contact and armature of relay 60 to ground. Relay isoperated in this circuit and closes a locking circuit for itself throughits continuity sprin and armature to ground at the uymerniosL frontContact and armature of relay 9. lVith relay 4O operated a source ofbusy tone current is connected with the calling line to inform thesubscriber there that the wanted party is busy. It will be rememberedthat the release relay of the register sender is locked operated throughits left-hand winding and a circuit controlled at the back contact ofrelay 42. Therefore when relay t0 energizes it opens this circuit andrelay 60 deenergizes to effect the release of the registers of thesender in the manner already outlined. In. the event that the callingparty first terminates the call by placing his receiver on itsswitch-hook, the relay 1S deenergizes and shortly afterwards theslow-releasing relay 9 retracts its armature and thereby opens theholding circuit 21 of the calling line switch. This permits relays 2 and6 to deenergize and relay 2 at its lower armature and back contact,close the operating circuit for the motor magnet 3 which restores theline switch to normal. Also when the relay 9 retracts its armatures itopens the operating circuit for the relay 7 8 and when this relaydeenergizes it opens the holding circuit for the called line switch,which circuit includes conductor 77. This permits the cut-off relay 67to deenergize and effect the release of the called line switch. In theevent that the called party first replaces his receiver on itsswitch-hook, the relay 87 retracts its armature and thereby closes acircuit from ground over conductor 88 and resistance to groundedbattery. This short-circuits relay 78 which opens the holding circuit ofthe called line switch, and effects the release in the manner described.The calling line switch,

however, is not released until relay 9 deen-- ergizes which is effectedby the restoration of the calling receiver to its switch-hook. "Whenrelay 78 deenergizes it closes a selfinterrupting circuit for motormagnet-46 which restores the frequency selector associated with thebridge circuit, to normal.

hen a subscriber desires to call a station on his own line, he dials aseries of impulses corresponding to the designation #100. In case thestation #2 is calling station number 3 or station #3 is calling station#2, thenv it is necessary to transmit a series of two impulses. Ifstation #2 is calling station #i or station #4 is calling station thenit is necessary to send three impulses If station is calling station #5or is calling' #2, it is necessary to transmit four impulses. If station#3 is calling station #4. or #a is calling #3, then five impu must besent. while if station #3 station #5 the dial is operated he send siximpulses; and if station #4 is calling station #5, or #5 is calling #4,seven impulses are sent. After dialing this fourth or last series ofimpulses the subscriber is instructed to hang up until his bell stopsringing or until he desires to abandon the Similarly an allotted finderswitch connects an idle register sender to the allotted bridge circuit.The subscriber first dials one impulse in response to which motor magnet46 of the frequency selector advances its brushes to their firstposition. At the close of this impulse the slow releasing relay 45 atitscontact and armature, connects the impulse circuit to the tens register.The subscriber thereupon transmits a series of ten impulses whichadvances the brushes of the tens register into their tenth position inthe manner previously described. Thereupon the subscriber transmitsanother series of ten impulses corresponding to the units designationwhich advances the units register brushes into their tenth position. Atest circuit is then completed to start into operation an idle revertivecall finder, such as is shown at the lower part of Figure 1. This testcircuit extends from a multi-contact relay to conductor 89, appearing atthe lower right-hand corner of Fig. 1, winding of relay 90, lower backcontact and armature of relay 91 to grounded battery. Relay 90 isenergized in this circuit and effects the operation of the finder byclosing a circuit from grounded battery,'resistance back contact,armature and winding of the magnet 92. uppermost armature and frontcontact of relay 90 to ground. Under the control of this circuit motormagnet 92 advances the brushes of the revertive call finder until thetest brush 192 encounters the test terminal 93 of the bridge circuittowhich the calling line has been connected, at which time relay 91 willbe operated and will close a locking circuit for itself. This currentextends from grounded battery at the inner, lower armature, frontcontactand lower winding of relay 91, conductor 94, inner armature and backcontact of slow releasing relay 95, conductor 96, holding brush 97 tothe holding conductor 21 of the selected bridge circuit. At thelowermost armature and front contact 98 of relay 91 the test circuit 89is extended to the next revertivc call finder of the series. to care forany succeeding revertive call. At the upper arniatul'es and frontcontacts of relay 91 break points are closed in the signalling circuitover which the fourth series at impulses are transmitted eperate thefrequency selector associated with the revertive call finder switch.Over this circuit ringing current of the proper frequency 1s firstapplied to signal the wanted station on the line, and then ringingcurrent of the proper frequency is applied tosignal the calling stationon this line.

This last-mentioned signalling circuit includes both windings of relay100 in series and as soon as the signalling circuit is closed, thisrelay attracts its armature thereby closing a circuit from ground at itsfront contact, back contact and armature of the motor magnet 104, brush105 in its'first pcsition, windingof the motor 'ma,g ;net104 to groundedbattery.

As a result of the closure of this circuit, the frequency selectoradvances its brushes into their first position in readiness to receivethe last series of mpulses correspondlng to the wanted sta' tion on theparty line.

The mentioned operations of the revertiye call finder follow thelast'series of ten im- "pulses, but before the calling subscribertransmits an additional series of impulses to select the current of theproper frequency. The calling subscriber now dials a series of twoimpulses corresponding to series No. 3 on his line. These impulses aretransmitted over the signalling circuit which extends from groundedbattery, upper windingot relay 100, back contact and armature of relay101, uppermost armature and front contact of relay 91, finder brush 102,conductor 15,1ine switch brush 14 and over lower side of calling linethrough the impulse contacts of the calling dial and over the upper sideof the-calling line, line switch brush 13, conductor 16, finder brush108, innermost upper front contact and armature of relay 91, innermostarmature and back contact of relay 101, lower winding of relay 100 toground. In response to the first of these impulses a circuit is closedfrom ground, armature and back contact of relay 100 slow releasingreback contact and armature of relay 100 to ground. The closure of thiscircuitis effective to advance the frequency selector into its thirdposition. Relay 107 is energized in this circuit and remains energizedduring this series of impulses.

Since it was assumed that a series of two impulses is transmitted tothis frequency selector, its brush 105, 109 and 118 will remain in theirthird pos tion. In the case of a re- 'vertive c'all, the'calling partyis instructed 'to hang up at the close of this series of impulses untilthe wanted party answers. Re

' lay 100 deenergizes whereupon switching reergized'a circuit is closedfrom ground,

brush 109, armature and back contact of relay95. uppermost trout contactand armature of relay 101, brush 123, conductor 124, winding of relay 17to grounded battery. Relay 17 is energized to maintain relay 18energized while the calling partys receiver is hung up during theringing period. Relay 18 holds relay 9 operated to prevent the releaseof the calling line'switch duringthis period. hen the switching relay101 operated it closes its contact 139 and armature to ground, therebyclosing a circuit including conductor 110 and the winding of relays 111and 112 through the contact 115 to grounded battery,whenever interrupter#1 has. rotated to the proper position. Similarly the circuit includingthe conductor 110, is completed through the windings 0t relays 113 and114, and the contact 116, whenever interrupter #2 is rotated into theproper position. It will be noted that the cam cuttings on theseinterrupters are so arranged that when interrupter-s 1 and 2 rotatethrough an eighth of a revolution from the POSllTlOllQllOWIl, they willactuate relays 111 and 112. 113 and 114 so that the 33 cycle source ofcurrent is applied to conductor 117 and thence through. brush 118 overthe conductor to signal station #3 on the calling line and back againover conductor 10 through the winding of trip relay to grounded battery.hen the interrupters are rotated through another quarter of arevolution, then only the relays 111 and 112 will be operated. so thatthe 16 cycle source oi ringing current is then connected to theconductor 117, which conductor in this instance is also included in theringing circuit just described. This alternate signalling of the callingand called subscribers stations continues until one of the partiesresponds. at which time the trip relay is energized and at its left-handtront contact and armature, closes a locking circuit for itself throughthe frequency selector brush 109 to ground. At the inner right handarmature and back contact of relay 95 the holding circuit of relay 91 isinterrupted to release the revertive call finder for use on t if) asucceeding call. This finder is of the stay-put type and it remains inengagement with the bridge last used. Also the operation of the triprelay closes a circuit for re toring the trequency selector to itsnormal position. This circuit is completed from grounded l 'ittery,winding oi the motor magnet 1.0%. conductor 108, right-hand armature andfront contact of relay 95, conductor 119. armature and back contact ofthe motor magnet, left hand front contact and armature of relay 95,brush 109 to ground. Under the control of this circuit the motor magnet10% advances the frequency selector until the same reaches its normalposition, which time the circuits to ground at brush 109 are opened andthe trip relay deenergizes to leave the frequency selector in readinesstor a succeeding call. As soon as this selector reaches its normalposition, the circuit of the switching relay 101 opened at brush 105causing it to release. l'his opens the holding circuit of relay 11'.Fig. 2, whereupon relay 17 releases to permit talking battery to heextended to both stations through the windings of relay 18.

111 this system a so-callerl overflow arrangement is provided so that itall the bridge circuits become busy, a busy signal is transmitted to thecalling subscriber until he releases or until a bridge circuit becomesidle.

lVhen all the bridge circuits are in use, all

thereby ground potential is disconnected from all the conductors such as19. Thereupon the low resistance relay 11 is energized in the circuitnow closed from ground, winding of this relay over any one of theconductors such as 19, upper armature and trout contact of a relaysimilar to 18 and winding of a relay similar to 9 to grounded battery.Relay 11 is operated in this circuit and at its inner arn'lature andback contact disconnects the stopping ground potential from the brush 10and opens the bridge allotter circuit at its outer armature and backcontact to prevent this allotter from continually rotating. This relayalso places a ground on the overflow test terminals of the lineswitches. which is applied at the lefthand armature and front contact ofrelay 11. It a :all is initiated when the above described conditionexists. the calling line switch will be advanced to the overflow trunkwhere relay will be operated by the closed circuit of the calling line.Relay 120 establishes a holding circuit for the line switch whichcircuit is opened when a tinder or bridge circuit becomes idle, thuscausing the line switch to leave the overflow trunk and. choose thebridge circuit which has become idle. As long as the line switch remainson'the overflow trunk, calling party receives a busy tone from source BZ indicating that the bridge circuits are all busy.

It the finders are all busy, relay 12 will be operated to open theoperating circuit of the finder allotter and to place a stoppingpotential on the test terminal of the overflow circuit so that thecalling line switch will he stopped in engagement therewith. When thisline switch seizes the overflow circuit, relay 120 is operated aspreviously described and applies a busy tone signal to the calling lineuntil the subscriber there abandons the call or a finder becomes idle.

In Figure 3 which appears at the lower left-hand corner of Fig. 2 thereis represented a two-way trunk extending from the common batteryexchange to an attendant operators position or station associated withthe private automatic exchange. In the case of this at endant stationthere is provided an individual switch similar to that provided tor eachof the lines of the private system. The brushes of this individualswitch are designated 132. 133, 134 and 135 and engage Let it first beassumed that a call from the main exchange is intended for somesubscriber in the private automatic exchange, In this case the callingsubscriber's line (not shown) will be extended either manually orautomatically to include the conductors of the trunk extending betweenthe main exchange and the branch exchange. As soon as this connectionhas been completed, signal 126 will notify the operator that the call isawaiting her attention. The operator thereupon depresses her listeningkey 127 by which her telephone set (not shown) is connected inductivelyto the incoming trunk and she receives the designation of the wantedstation. As soon as the listening key 127 is depressed, the relay 128 isoperated in a circuit including the operators telephone set and closes acircuit from ground, its outer frontcontact, armature and left-handwinding of relay 129 to grounded battery. This last named relay isoperated and closes a circuit from ground, its outer front contact andarmature, winding of the motor magnet 130, its armature and backcontact, through the resistance to grounded battery. Under the controlof this circuit the motor magnet advances the brushes 132 to 135inclusive to select an allotted bridge circuit in the manner previouslydescribed for a subscribers line of the private exchange. When theallotted bridge circuit is located, the relay 131 is operated in acircuit traceable from grounded battery through the resistance, backcontact and armature of the motor magnet, right-hand winding, innerarmaturel ill) and front contact of relay 129, armature and back contactof relay 12S, oil normal contacts 136 brush 135, the outgoing terminalof the allotted bridge circuit over a conductor similar to 8 of Fig. 1to ground as previously described. This last described circuit shortcircuits the motor magnet 130 and stops the line switch in engagementwith the allotted bridge circuit. Also when relay 131 is opt erated itextends the operators telephone set to holding conductor similar to 21.

through its front contacts and armatures to brushes 132 and 133 of theline switch. These, brushes will thereupon extend the circuit toconductors similar to'15 and 16 of Fig; 1 to serially include bothwindings of a. relay similar to 18 appearing at the upper left-handcorner of Fig. 2. The operation of relay 18 will energize a relay 9 aspreviously described to apply a. holding ground The relay 131 ofFig. 3is thereupon locked operated over acircuit completed from groundedbattery, lower winding which in the case of the attendants position isof low resistance, inner front contact and armature of this relay andholding brush 134: which is in engagement with a holding terminalassociated with the seized bridge circuit and connected to the holdingconductor 21.

The operator thereupon operates the dial sender 136 to set up thedesignation of the wanted station on the register sender. WVhereupon theconnection is completed in the manner that has been described inconnection with calls within the private auto-' j the short circuit isremoved from relay 140 andalthough it is marginal it operates in serieswith the lower winding of relay 131', and the circuit of the called lineis effective to hold relays 128 and 18 operated because the condensersare short-circuited. However, in the case of calls within the exchangethe relaycorresponding to 131 has its lower 'inding of high resistanceso that marginal relay 140 will not operate in the series therewith andconsequently will not short circuit the condensers of the bridgecircuit.

Supervision. at the main exchange is also permitted by reason of thefactthat in case of calls that originate outside of the privateautomatic exchange, relay l iO short-circuits the condensers whichnormally conductively separate two sides of each bridge circuit as :hasbeen described. With relay 1 1-0. operated and the condensersshort-circuited, the called party at the automatic exchange on hangingup his receiver will actuate a signal at the main exchange, in the caseof a manual connection whereas in the case of an automatic connection heeliects the deenergization ofa relay to give supervision in the mannerwell known.

The release of the switches of the private automatic exchange in thecase of a call originating at a main otiice is also controlled by thecalled party placing his receiver on the switch-hook. This will causethe relay corresponding to 87 to retract its armature and therebyshort-circuit relay 78in the manner previously described. Relay 78 ondeenergizing opens the holding circuit 77 of the called line switchwhich thereupon releases, as has been described. This also releasesrelays 128 and 18 and the line switch of the Figure 3. The release ofthat portion of the connection completed at the main oflice may beeffective in any Well known mannor. 7

Since the trunk as represented in Fig. 3 is of the character referred toas a two-way trunk, when a subscriber at the private automatic exchangedesires to obtain a connection at the main exchange, the line switch ofFig.

may be operated in response to a predetermined setting of the registersender whereupon the calling subscriber can then dial impulses to setautomatic switches at a distant automatic exchange, or in the case thatthis exchange is manual, an operater is signalled.

lVhat is claimed is: t V

1. In an automatic telephone system in combination with a plurality oftelephone lines, bridge circuits means for assigning bridge circuits foruse ahead of the calls, means including a non-numerical switch forextending telephone lines to either end of an assigned bridge circuit, aplurality of senders, means for assigning senders for use, means forassociating an assigned sender with an assigned bridge circuit, meansfor adjusting said sender from a remote point, and means operating underthe control of said adjusted sender for controlling the extension of awanted line to said assigned bridge circuit.

2. In an automatic .telephone system, in combination with a plurality oftelephone lines, line switches for said lines, bridge circuits, meansfor assigning bridge circuits for use aheadot' the calls, means forcausing the switch of a calling line to extend the same to an assignedbridge circuit, a plurality of senders, meansfor assigning senders foruse, means for associating the assigned sender with an assigned bridgecircuit, means for adjusting said sender from a remote point inaccordance with the designation of the wanted line, and means operatingunder the control of said ad usted sender'for causing the line switch ofa wanted line to extend the same to said assigned bridge circuit.

3. In an automatic telephone system, in combination with a plurality oftelephone lines, an individual switch for each of said lines, bridgecircuits each provided with two branches both terminating in eachswitch, means for allotting bridge circuits for use ahead of the calls,means for causing the line switch of a calling line to seize theoutgoing branch of said allotted bridge circuit, a plurality of senders,means for assigning senders for use, means for associating an allottedsender with an allotted bridge circuit, means for adjusting said senderfrom a remote point in accordance with the designation of av wantedline, and means operating under the control of said adjusted sender forcausing the individual switch of the called line to seize an incomingbranch of the allotted bridge circuit.

4. In an automatic telephone "system, in combination with a plurality oftelephone lines, an individual switch for each telephone line, aplurality of bridge circuits each provided with incoming and outgoingbranches terminating in each of said switches, a progressively movableswitch for allotting bridge circuits for use ahead of the calls, meansfor causing the individual switch of a calling line to seize theoutgoing branch of an allotted bridge circuit, a plurality of senders,means for assigning senders for use, means for associating an assignedsender with an allotted bridge circuit, means for adjusting said senderfrom a remote point in accordance with the designation of a wanted line,and means operating under the control of said adjusted sender forcausing the individual switch of tl e called line to extend the same toan incoming branch of said allot ted bridge circuit.

5. In an automatic telephone system, in combination with a plurality oftelephone lines, a plurality of telephone stations on each of saidlines, each station being provided with a signal responsive to currentof certain frequency, a plurality of bridge circuits, means forallotting said circuits for use.an individual non-numerical switch foreach telephone line operative on the initiation of a call on its line toextend the same to an allotted bridge circuit, sources of current ofdifferent frequencies, a frequency selector directively controlled overa calling telephone line to select a source of current of the properfrequency to signal the wanted station, a sender directively adjustableover a calling telephone line in accordance with the designation of awanted telephone line, means responsive to the adjustment of said senderfor causing the line switch of the desired line to seize the allottedbridge circuit, means responsive to said seizure to apply the selectedsource of current to said wanted line 7 nection.

6. In an automatic telephone system, in combination with a plurality oftelephone lines, a plurality of stations on each of said lines, eachstation being provided with a signal responsive to current of a certainfrequency, a plurality of bridge circuits,means for allotting saidbridge circuits for use, an individual non-numerical switch for eachline operative on the initiation of a call on its line to extend thesame to an allotted bridge circuit, sources of current of differentfrequencies, a frequency selector directively controlled over a callingtelephone line to select a source of current of the proper frequency tooperate the signal at the wanted station, a sender directivelyadjustable over the calling telephone line in accordance with thedesignation of the called line, said sender being adjusted subsequent tothe operation of said frequency selector, means responsive to theadjustment of said sender for causing the line switch of the desiredline to seize the allotted bridge circuit, means responsive to saidseizure to apply the selected source of current to said line and meansfor releasing the established connection.

7 In an automatic telephone system, in combination with a plurality oftelephone lines, a plurality of stations on each of said lines, eachstation being provided with a signal responsive to current of a certainfrequency, a plurality of bridge circuits, means for allotting saidbridge circuits for use, an individual non-numerical switch for eachline operative on the initiation of a call on its line to extend thesame to an allotted bridge circuit, sources of current of differentfrequencies, means directively controlled over a calling telephone lineto select a source of current of the proper frequency to operate thesignal at the wanted station, a sender directively adjustable over thecalling telephone line in accordance with the designation of the calledline, said sender being adjusted subsequent to the operation of saidfrequency selector, means responsive to the adjustment of said senderfor causing the line switch of the desired line to seize the allottedbridge circuit, means responsive to said seizure to apply the selectedsource of current to said line, means for releasing said sender forcommon use as soon as the individual switch of the wanted line hasseized said allotted bridge circuit, and means for releasing theestablished connection.

8. In an automatic telephone system, in combination with a plurality oftelephone lines, a plurality of stations on certain of said lines, eachof said stations on a telephone line being provided with a signalresponsive to current of a certain frequency, a plurality of sources ofcurrent of the proper frequency to operate each of said signals, afrequency selector for selecting the proper frequency to operate asignal at a wanted station, a non-numerical switch responsive to controlfrom a remote point for associating said frequency selector with acalling line, means controlled over said calling line for variablyoperating said selector to connect the proper source of current to acalling line to signal a wanted station thereon and means for releasingsaid non-numerical switch prior to the termination of the call.

9. In an automatic telephone system, in combination with a pluralityoftelephone lines, a plurality of stations on certain of said lines,each of said stations on a telephone line being provided with asignalresponsive' to current of a certain frequency, a plurality of sources ofcurrent of the proper frequency to operate each of said signals,non-numerical switches for said telephone lines, a plurality of bridgecircuits, anyone of which is arranged to be seized by a nonnumericalswitch, a sender, means for associating said sender with a selectedbridge circuit, means for variably operating said sender over a callingline and bridge circuit in series, a frequency selector, a non-numericalswitch associated therewith, means operated in response to apre-determined setting of said sender for causing said non-numericalswitch to associate said frequency selector with a calling line, meanscontrolled over said calling line for directively operating saidfrequency selector to apply a source of current of the proper frequencyto signal the, wanted station on the calling line, and means forreleasing said established connection.

10. In an automatic telephone system in combination with a plurality oftelephone lines, non-numerical switches for the use of said lines, aplurality of bridge circuits each having incoming and outgoing branchesterminating in each of said switches, a test brush for eachnon-nmnerical switch, means for rendering said test brush effective totest outgoing branches of said bridge circuits when its telephone lineis callingmnd means for rendering said test brush effective :to testonly incoming branches of said bridge circuits when its telephone lineis being called.

11. In an automatic telephone system n combination with a main exchange,a branch exchange, telephone lines terminating at said branch exchange,an operators position at said branch exchange, a trunk circuit extendingbetween said main .exchange and said operators position, non -numericalswitching means associated with said operators position forautomatically extending a call from said trunk circuit to a wantedtelephone line and from a telephone line to said trunk,andmeanscontrolled over said telephone line for disestablishing aportion of the connection.

12. In an automatic telephone system, in combination with a mainexchange, a branch exchange, telephone lines terminating at said branchexchange, an attendant operators position at said branch exchange, atwo-way trunk circuit extending between said main exchange and saidoperators position, means including a nonqnnnerical switch forautomatically extending any one of said telephone lines as a callingline over said trunk circuit to the main exchange, means including saidnon-numerical switch associated with said operators position, forextending a call from said trunk circuit to a wanted telephone line, andmeans controlled over said wanted-telephone line for disestablishing aportion of a connection.

13. In an automatic telephonesystem, in combination with a telephoneline, a plurality of stations on said telephone line, each of saidstations being provided with a signal responsive to current of differentcharacter from that to which the other stations are responsive, aplurality of bridge or link circuits, a non-numerical switch forextending said telephone line to a bridge circuit, sources of current ofdifferent character for actuating said signal, a numerical switch. meansfor associating said last-mentione .l switch with said bridge circuitand means for operating the same over said telephone line, meansresponsive to the setting of said numerical switch for applying theproper source of current to said telephone line to signal the callingand wanted stations thereon, andmeans for releasing said numericalswitch before termination of the conversation.

1 1. In an automatic telephone system, in combination with a telephoneline, a plurality of stations on said telephone line, each of saidstations being provided with a signal responsive to current of dillerent frequency from that to which the other stations are responsive, aplurality of bridge circuits. a non-numerical switch for extending saidtelephone line to a bridge circuit. sources of current of differentfrequency for actuating said signal, a numerical switch, means forassociating said last-mentioned switch with said bridge circuit andmeans for operating the same over said telephone line, means responsiveto the setting of said numerical switch for alternately applying theproper sources of current to said telephone line to signal the callingand wanted stat-ions thereon, and means for releasing said numericalswitch before the termination of the conversation. V

15, In an automatic telephone system, in combination with a. telephoneline, a pinrality of stations on said telephone line, each of saidstations being provided with a, sigltll) nal responsive to current ofdilferent character from the other stations, a bridge circuit, a sourceof talking current connected to each bridge circuit, a non-numericalswitch having terminals in which said telephone line and bridge circuitterminate, numerical switch connectible to said bridge circuit andresponsive to directive control over said telephone line, meansresponsive to the setting of said numerical switch for selecting sourcesot'current of the proper frequency to signal the calling and wantedstations on said wanted telephone line, and a conversational circuitincluding said telephone line and bridge circuit but having only oneautomatic switch therein.

16. In an automatic telephone system, a plurality of telephone lines, aplurality of nonnumerical switches, a plurality of bridge circuits,means for causing a non-numerical switch to extend a calling telephoneline to an assigned bridge circuit, a plurality of senders, means forassigning senders for use, means for associating the assigned senderwith an assigned bridge circuit, means for adjusting said assignedsender from a remote point in accordance with the designation of thewanted telephone line, and means operative under the control of saidadjusted sender for causing a non-numerical switch to extend a calledline to said assigned bridge circuit.

17. In an automatic telephone system, a plurality of telephone lines, aplurality of telephone stations on each of said telephone lines, each ofsaid stations being provided with a signal responsive to current of acertain characteristic, a plurality of bridge circuits, a plurality ofnon-numerical switches, means including at least one of saidnonnumerical switches for extending a calling telephone line to a bridgecircuit on the initiation of a call, sources of current of differentcharacteristics, means controlled over the calling telephone line andbridge circuits for causing a non-numerical switch to extend a calledtelephone line to said selected bridge circuit and means directivelycontrolled for connecting current of the proper characteristic to signalthe wanted station on the called telephone line.

18. In an automatic telephone system, a plurality of telephone lines, aplurality of stations on each of said lines, each of said stations beingprovided with a signal responsive to current of a certaincharacteristic, a plurality of bridge circuits, a plurality ofnon-numerical switches, means including a non-numerical switch forextending a calling telephone line to a bridge circuit, sources ofcurrent of different characteristics to actuate said signals, afrequency selector directively controlled over a calling telephone lineto select a source of current of the proper character to actuate thesignal at the wanted station, a sender directively adjustable over thecalling telephone line in accordance with the designation of the calledline, said sender being adjusted sub sequent to the operation of saidfrequency selector, means responsiw e to the adjustment of said senderfor causing a non-numerical switch to extend the wanted telephone lineto the selected bridge circuit, means respon sive to said extension toapply the selected source of current to said telephone line, and meansfor releasing the established connection.

19. In a telephone system, a plurality of telephone lines. a pluralityof bridge circuits, an over-flow circuit, a plurality of nonnumericalswitches, means including a nonnumerical switch extending a callingtelephone line to a bridge circuit on the initiation of a call, andmeans directively controlled for causing a non-numerical switch toextend the wanted telephone line to the bridge circuit to which thecalling line is connected, means for rendering the bridge circuit busywhen it is seized by a nonnunierical switch, and means operative whenall of said bridge circuits are busy for causing said non-numericalswitch to extend a calling telephone line to said over-flow circult.

20. In an automatic telephone system, a main exchange, a local exchange,an operators position at said local exchange, a plu rality of telephonelines terminating at said local exchange, means including a plurality ofautomatic switches for interconnecting said telephone lines, meansincluding a trunk circuit for extending a call from said main exchangeto said operators position, a nonnumerical switch associated with saidtrunk circuit, and means including a non-numerical switch and certain ofsaid automatic switches for extending said trunk to any of saidtelephone lines and for extending any of said telephone lines to saidtrunk.

In witness whereof, I hereunto subscribe my name this 9th day of March,A. D. 1921.

VVINFRED T. POWELL.

